1. Field of the Invention
The present invention relates to the field of pushbutton radio tuners and more specifically to obtaining improvements in repeatable tuning accuracy as well as decreasing frictional forces in the tuner assembly.
2. Description of the Prior Art
Over the past several years, many attempts have been made to reduce the size of conventional radio tuners, so that they will take up less space in vehicle dashboards and also achieve a beneficial weight reduction.
In U.S. Pat. No. 3,863,509, a relatively flat tuner design is shown, whereby reactance coils located in one end of the tuner are changed in position and tune stations, over a selected band, by movement of a flat bolt. The flat bolt is caused to translate in an arc generally orthogonal to the movement of pushbuttons mounted to slide in and out of the front of the chassis. Interaction between the pushbuttons and the flat bolt occurs due to cams mounted on the pushbuttons and cam follower devices mounted for rotation on the chassis. Several cam followers are mounted on the chassis and are each associated with a corresponding pushbutton. Therefore, when a pushbutton is depressed, the cam mounted thereon interacts with the corresponding cam follower and causes it to rotate about a pivot extending from the chassis. The other end of the cam follower has a pin which extends through apertures in the flat bolt and moves through an arc when the cam follower rotates to define the arcuate movement of the flat bolt. In this patent, several springs are used to take up slack in the linkage between the chassis, cam follower, and flat bolt. Consequently, sufficient friction is present between each pivotal connection to cause the mechanism to be tight and require high forces to be applied to the pushbuttons in order to effect tuning of the radio.
U.S. Pat. No. 3,946,344 is directed to a relatively flat radio tuning mechanism, whereby cam followers are mounted on pivots extending from the top of a chassis and are, in turn, pivot connected to a translating flat metal strip. The flat metal strip is movable along an arc to effect tuning of the radio. As in the previously discussed patent, each of the pin connections from the cam followers to the flat metal strip is spring biased. Each pivot connection of a cam follower to the top of the chassis is via a cylindrical stud extending from the cam follower through matching holes on the upper plate of the chassis. It is apparent that in order for tuning accuracy to be maintained in a repeatable manner, the holes in the top plate of the chassis must be machined to a close tolerance and thereby present some friction to rotation of the cam follower.
It can be seen from the two patents discussed above, that desirable accuracy in repeatable tuning is accompanied by the disadvantage of high resistance forces to tuning.